In the art of gears there exists many types of gear arrangements. Gear teeth can vary in form from spur and helical, to worm, bevel, and hypoid shapes. Further, the shafts around which the gears rotate can vary in relative arrangement from parallel, to skew or intersecting.
Generally, gears are made from a strong and durable material able to withstand the repeated sliding contact and pressure loads between gear teeth relative to a load placed on the gears. In addition, gears are most commonly mounted to a structure or housing, such that each gear may only rotate about one axis. Typically, gears in contact are also mounted such that their centers remain a fixed distance from each other. As a result, gears are constructed such that the teeth, when they mesh with the teeth of mating gears, have a predetermined amount of play, or backlash. This backlash allows the teeth of mating gears to mesh together and part as the gears rotate.
Backlash, in its simplest terms, is the difference in the width of a gear tooth space from the width of a mating gear tooth, measured at a pitch circle or pitch plane. The pitch circle or pitch plane is an imaginary circle or plane that rolls or moves without slippage with a pitch circle or pitch plane of a mating gear.
In some applications of gears, it is of great importance to rotate, or move, a particular object such as a platform, with a combination of gears, such that a resulting location of the platform is precise relative to a predetermined target location. By precise, what is meant is within an acceptable margin of error for an application. A shortcoming of a typical combination of gears is that the built-in backlash, required to allow the gear teeth of mating gears to engage and disengage, results in the platform being moved non-precisely such that the resulting location is not the target location within an acceptable margin of error.
Attempts have been made by means of various methods to address this seemingly inherent characteristic of backlash in gears. An attempted solution to cure backlash in worm gears has been generally to use a joint at one end of a worm gear, and a spring at the other end pulling the worm gear toward a mating worm wheel. A shortcoming related to this type of arrangement involves the lack of control over axial movement of the worm gear. An additional shortcoming is a lack of control over torsional forces on the worm gear resulting from the pressure of the spring, which impairs the accuracy and/or repeatability of the rotary positioning of the platform or attached movable object.